Piezo-electric apparatus



Feb. 12, 1935. GQLDSTINE 1,990,822

PI EZO ELECTRIC APPARATUS Filed March 14, 1932 2 Sheets-Sheet 1 N. E GOLDSTINE I v i ATTORNEY Feb. 12, 1935. E, GQLDSTINE 1,990,822

PIEZO ELECTRIC APPARATUS Filed March 14, 1932 2 Sheets-Sheet 2 INVENTOR H.E.GOLDS INE BY ATTORNEY Patented Feb. 12 1935 PATENT OFFICE PIEZO-ELECTRIC APPARATUS Hallan E. Goldstine, Rocky Point, N. Y., assignor to Radio Corporation of America, a corpora- .tion of Delaware Application March 14, 1932, Serial No. 598,622 6 Claims. (01. 171-327) This invention relates to improvements in piezo-electric crystal apparatus.

It is well known in the art that the free vibrations of a piezo-electric crystal element set up strains and stresses which are substantially proportional to the voltages applied thereto. These stresses in the crystal element are frequently unsymmetrical due to the non-uniformity of the thickness of the element and the presence of different electro-motive forces on adjacent portions of the crystal. This unsymmetry, it has been found, is an undesirable characteristic which should be avoided for best results, particularly so in systems wherein a plurality of electrodes are utilized on the same side of the crystal. In this case slight differences in the thickness at various points on a crystal and varying piezo-electric properties of the material tend to cause considerable variation in relative voltages set up on the electrodes. Accordingly, it is a desideratum that the electro-motive forces of each electrode be applied to the crystal over as wide an area as possible and that the areas used be variable in order that more uni- 25. form voltage ratios may be obtained with various individual crystals used with the same holder and electrodes or with holders and electrodes of the same design.

One method of overcoming this diificulty is described and claimed in a copending application of C. W. Hansell Serial Number 588,255 filed January 23, 1932. Briefly, the method of the above entitled application comprises constructing the electrodes adjacent one face of the 35 crystal element in such manner that each electrode covers rather widely separated areas which are unsymmetrical with respect to any one plane passing through the crystal. In this way the respective electrodes affect, simultaneously, widely separated points of the crystal and aid in securing a uniform piezo-electric coupling eflect between the electrodes. In such an arrangement however, undesirable capacity effects may occur between the electrodes and their associated circuits due to the close proximity of the electrodes to each other. One of the objects of the present invention is to overcome this difiiculty.

A'further object of the present invention is to obtain a very high degree of adjustment between the piezo-electric crystal and its. associated electrodes. This is effected by providing a novel movable crystal retaining element for changing the relative areas of the crystal facing the electrodes. In this manner the crystal may be positioned for optimum oscillation to present the best feed-back and electrode area for a particular resonator.

A feature of this invention is the shielding arrangement provided between the electrodes positioned on the same side of the crystal to prevent undesirable capacity coupling effects. This arrangement efiectively reduces energy leakage and produces a screening action between circuits.

Another feature is the adjustable electrode support which enables movement of one electrode with respect to any other electrode positioned on the same side of the crystal. By means of this feature the reactance between the crystal and the electrode maybe changed, thus permitting to some extent, control of the voltages generated.

Other objects, features and advantages will appear in the subsequent detailed description.

In the accompanying drawings, Figures 1 and 2 illustrate plan views of unsymmetrically arranged electrode structures having shielding between electrodes.

Fig. 3 illustrates a cross sectional plan view of the rotatable crystal retaining means, the section being taken on lines 3-3 of Fig. 4.

- Fig. 4 is a side view in cross section of the apparatus of Fig. 3 along the line 4-4.

I Fig. 5 is a modification of the apparatus of Fig-3.

Figs. 5a and 5b are side and plan views respectively of the spacing pins used in Fig. 5 for holding the crystal in position.

Fig. 6 is a further modification of the apparatus of Fig. 3.

Fig. 6a is a plan view of the off-center (eccentric) star arrangement utilized for holding the crystal of Fig. 6 in place.

Fig. 7 illustrates the adjustableelectrode support, which enables movement of one electrode with respect to any other electrode positioned on the same mounting.

Fig. 8 shows diagrammatically a circuit arrangement wherein there is utilized a piezo-electric crystal structure embodying the principles of the present invention.

In Figs. 1 and 2 are shown two electrode mountings, each comprising unsymmetrically arranged electrodes 1 and 2 of the inter-laced comb and square inter-woven spiral type respectively, mounted on a suitable insulating disc 3. These electrodes may be attached to the insulating disc 3 either by screws or by being molded therein. The surfaces of the two electrodes 1 and 2 diifer in area at different portions thereof in the manner indicated in the drawings and are arranged to be unsymmetrical with respect to any plane passing through the mounting or the crystal. In this manner each electrode presents a surface which faces widely separated portions of the crystal so that closely spaced points of the crystal at different parts thereof face different electrodes. It will .beapparent that any rotation or movement either of the electrode mounting or of the, crystal will change the relative areas of the crystal facing the two irregularly shaped electrodes.

Between the electrodes 1 and 2' and insulated therefrom is a conducting shield 4 for reducing the undesirable capacity efiects between the closely spaced electrodes. This shield may comprise a metallic bar or a ladder-like grid or any other suitable shielding material. If desired,

' shielding screen 4 may extend around the outer edges of the electrodes in the manner shown in the drawings. This shield is arranged to have a thickness and height above insulating disc 3 atleast equal to'the' thickness of thev raised portion of the electrodes, and may be attached to the electrode mounting in any desired fashion such as by screwsor by being molded therein. Fig. 3 shows, essentially, a device for rotating thecrystal in the holder and orienting the same under the upper unsymmetrical electrodes in order to obtain the best output. This device comprises a movable, retaining ring 5 which may be of insulating or conducting material having prongs 6, 6 for holding the crystal in place. The

retaining ring 5 is secured to the lower electrode by retaining studs 5A and 5B. Formed from the same piece as the movable retaining ring is a handle or manipulating arm 7 which is adapted to be rotated over a slotted sector element 8 attached to housing ring 9 by screws 8A and 8B. Passing through the arm '7 and slotted sector 8 is a clamping screw 10, which is utilized for holding the retaining ring in a desired position by a locking nut 10A retained in the groove 1013.

Although the sector shown in the drawings subtends an angle of about 20 it is to be understood that this element may subtend a greater angle if desired. It will be evident that the lower electrode; upon which the retaining ring is mounted, may-be attached to the retaining ring, if desired, and consequently be movable with the retaining ring. In the latter arrangement care must be taken to insulate the retaining ring and sector from the electrodes above the'crystal.

Fig: 5 is'a modification'of-the apparatus of Fig. 3 and shows a plurality of adjustable spaced pins 11, 11 for holding the crystal inplace. The spacing pins 11 are of metal such as brass and are adapted to be forced snuglyinto holesdrilled into the lower electrode and are turned to a position to fit any one of a wide variation inv sizes ofpiezo-electric elements} These pins may ,be made up in a numberof different forms to set crystals of different shapes and sizes. As shown in the drawings, the pins have a cam shape. Screws 12 may be usedfor holding the individual pins in place.

Fig. 6 is a further modification of the apparatus of Fig. 3 and showsan off-center (eccentric) star arrangement for holding various crystals in place.

Fig. '7 shows in cross section an electrode mounting which is adapted to vary the spacing between the crystal and one of the two electrodes 1, 2-. In the drawings, electrode l'is shown attached to an adjustment screw 13' and can be raised or lowered for changing the reactance betweenthe crystal and the movable electrode, thus enabling control of the voltages generated.

.Although this particular form of variable means is shown for varying the spacing between electrode 1 and the crystal it will be understood that any suitable apparatus may be utilizedfor acv complishing the same purpose. In this figure the electrodes are shown properly screened by shields 4, 4.

Although only two upper electrodes and the shield 4 are shown in the drawings it will be evident that any desired number of electrodes may be mounted on the insulating disc.

In Fig. 3 is shown an oscillation generator circuit of the type described and claimed in copending application Serial Number 531,684, filed by J...L. Finch April 21, 1931, wherein this invention may be employed. In this circuit there is shown 'a screen grid vacuum-tube'oscillation generator 14 having the usual anode electrode 15, control electrode 16 and filament 13 provided with the usual filament current supply source 17 and anode'voltage supply sources 18. Con denser 19 is provided to shunt the radio frequency currents in the anode circuitaround'the voltage source 18. Associated with anode is a plate impedance 20 connected to the output circuit. To this impedance is connected lead 21 which connects with electrodel of the piezo-' electric crystal apparatus. Control electrode 16 of the generator 14 is shown connected to the other upper electrode 2 of-the apparatus. Both electrodes 1 and 2 are of the unsymmetrical type; The screen grid 28 of the generator is shown connected on one sideto battery 18 and on the other side by means of shielding to shield 4 placed between the two symmetricalelectrodes for reducing undesirable capacity eifects. Leads 22 and 23 are also shown connected to shielding element 4 to efiectively screen the'circuit from deleterious leakage of energy atclosely spaced parts of'thecircuit. g

The operation of this circuit is as follows: Voltage waves impressed on control grid 16 of the tube 10 are amplified inthe tube and are,

in turn, impressed upon the resistor'circuit 20 by anode 15. Energy isfed from theoutput circuit 20 and impressed onthe electrode 1,

setting up a voltage between electrodes 1 and 24. r

2 and 24. These voltages are introduced in the I input circuit 26, which'is arranged toimpress voltage waves on the control grid 16 identical with those originally'assumed. Thus thiscircuit will sustain oscillations, and; if other conditions are correct will build up oscillations-from an initial nonoscillating state at the frequency or close to theresonant frequency of 'the'crystal. The output of this generat'ormay betaken off by lead 27. 1 1 In this circuit one may obtain optimum operation of the circuit by moving the crystal retaining ring by such means: as is. disclosed in Figs. 3 and 5 to obtain the desired relative voltages on the primary and secondary electrodes v1 and 2 for building up and sustaining oscillations. in the circuit. Consequently, use may now. be made of any crystal which heretofore did not conform to the proper standard and fewer crystals must be rejected. With this arrangement there is a uniformity of operating adjustments which helps to make the frequency of the oscillations less subject to influences tending to change the frequency.

It should be noted that, in the circuit, of Fig. 8, the piezo-electric crystal and its electrodes really constitute a filter between the anode and control grid circuits which passes an extremely narrow band of frequencies and it is this filter action which prevents production of oscillations at a frequency much difierent from the natural period of the crystal. This arrangement of variable unsymmetrical electrodes actually serves to make variable the effective characteristic impedance inside the crystal filter and its efiective relative terminal impedance at its input and output ends.

What is claimed is:

1. A piezo electric crystal holder having, in combination, an adjustable crystal mounting, said mounting comprising a retaining ring having means for holding the crystal in place and locking means for securing said retaining ring to said holder.

2. A piezoelectric crystal holder having in combination, a plurality of electrodes, a rotatable crystal mounting adapted to be placed upon one of said electrodes, said mounting comprising a circular retaining ring having a manipulating arm, said retaining ring having means for holding a crystal in place, a slotted sector attached to said holder under which said arm is adapted to move, and locking means extending through said arm and into a slot in one of said electrodes for securing said ring to said holder.

3. A piezo electric crystal holder having in combination, a plurality of electrodes, at least one of said electrodes being rotatable, a mounting adapted to be placed upon said electrode, said mounting comprising a circular retaining ring having a manipulating arm, said retaining ring having means for holding a crystal in place, a slotted sector attached to said holder under which said arm is adapted to move, and locking means extending through said arm and into a slot in one of said electrodes for securing said ring to said holder.

4. An electrode mounting for piezo electric crystal apparatus comprising a base and a housing ring, an insulating disc within said housing ring having a plurality of electrodes attached thereto, at least one of which is a movable electrode adapted to be raised or lowered with respect to said other electrode.

5. In piezo electric crystal apparatus, comprising a crystal and a plurality of electrodes on the same side of the crystal, means for varying the spacing vertically between the crystal and one of the electrodes on the same side of the crystal comprising adjustable means attached to said one electrode for moving said one electrode with respect to said crystal.

6. An electrode mounting for a piezo electric crystal comprising a crystal and a plurality of intercalated electrodes positioned on the same side of said crystal and shielding means positioned between and in the same plane as said electrodes and insulated therefrom.

HALLAN E. GOLDS'I'LNE. 

